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Diarrhoea can be caused by a wide variety of mechanisms:
• If the intestinal lining becomes irritated, it can fail to reabsorb fluid and nutrients effectively.
• An inflamed or irritated intestinal tract may also secrete excess fluid.
• If food travels though the intestine too rapidly, this does not allow for re-absorption of liquid.
A number of factors may give rise to these effects.
• Infectious diarrhoea is caused by ingesting microscopic viruses, bacteria or parasites, which then live in the intestine. These microbes are usually passed on through casual contact with infected people. These disorders, characterised by inflammation of the mucous membrane, are often referred to as dysentery.
Food is an ideal medium for the proliferation of infective agents. Unhygienic practices such as neglecting to wash one's hands when working with food, cross-contamination of foods in the same kitchen, inadequate cold-storage facilities, and repeated reheating of foods all contribute to microbiological growth.
In these cases, diarrhoea may have a positive effect in that it helps to rapidly expel dangerous microbes from the digestive tract.
- Viral infection is probably the most common cause of short-term diarrhoea. A virus damages the mucous membrane lining the intestine and disrupts fluid absorption. Rotavirus is often the cause of diarrhoea in children under two. Norwalk virus is more common in adults, and usually results from drinking contaminated water or food.
- Bacteria in contaminated food or water produce toxins that trigger intestinal cells to secrete salt and water, resulting in diarrhoea. Salmonella, Campylobacter, Listeria and Shigella are serious foodborne bacterial infections that require medical evaluation. Diarrhoea caused by E. coli most often occurs in visitors to developing countries where sanitation is poor. Cholera, which has acute diarrhoea as one of its symptoms, is contracted mainly by drinking contaminated water.
- Parasites such as amoeba and giardia can attack the intestine. Giardia may occur in wild animals and contaminated water. Giardiasis usually infects young children, often in day care, where it is transmitted by direct contact, or by adults changing different children’s nappies without hand washing. Giardiasis can last months without treatment and spreads rapidly. Testing all contacts is important, as some people spread the infection without having diarrhoea themselves.
- HIV-positive individuals are also at risk of other opportunistic infections that can cause diarrhoea, e.g. cryptosporidium and isospora belli.
Non-infectious diarrhoea
• Food: Certain foods may cause diarrhoea in some people, for example large amounts of alcohol, caffeine, artificial sweetener, or fatty or spicy foods.
Many people are intolerant of the milk sugar lactose, due to lactase deficiency. Lactase is an enzyme that breaks down lactose to glucose, which is readily absorbed by the intestinal tract. Even small amounts of dairy products can cause diarrhoea in individuals with lactase deficiency.
• Medications: Diarrhoea can develop up to a month after taking antibiotics. Antibiotics change the gut microflora and can predispose to infection with a bacteria called Clostridium difficile, resulting in diarrhoea that can range in severity from a mild illness to life-threatening disease.
Many people become dependent on chemical laxatives such as milk of magnesia, magnesium sulphate (Epsom salts), cascara and phenolphthalein. Magnesium can be inadvertently ingested in certain over-the-counter products. Sorbitol, an artificial sweetener used in some products such as jams, is also a laxative.
If diarrhoea occurs after taking a new medicine, contact your doctor.
• Diseases: Chronic diarrhoea can be caused by intestinal disorders such as inflammatory bowel disease (including ulcerative colitis and Crohn's disease), chronic pancreatitis, coeliac disease, colon cancers and tumours of the small intestine. Microscopic colitis is an unusual condition which causes diarrhoea in elderly people. These are serious diseases requiring medical attention.
Irritable bowel syndrome (IBS) is a very common cause of diarrhoea and occurs when the intestine does not contract smoothly and rhythmically. The contractions can be too strong, causing diarrhoea, or too weak, causing constipation. There may be alternating constipation and diarrhoea. IBS is associated with abdominal pain and bloating. Emotional stress may aggravate these symptoms.
Diabetes mellitus, kidney disease and a history of intussusceptions (where one portion of the bowel “telescopes” into the next) can also cause chronic diarrhoea.
• If the intestinal lining becomes irritated, it can fail to reabsorb fluid and nutrients effectively.
• An inflamed or irritated intestinal tract may also secrete excess fluid.
• If food travels though the intestine too rapidly, this does not allow for re-absorption of liquid.
A number of factors may give rise to these effects.
• Infectious diarrhoea is caused by ingesting microscopic viruses, bacteria or parasites, which then live in the intestine. These microbes are usually passed on through casual contact with infected people. These disorders, characterised by inflammation of the mucous membrane, are often referred to as dysentery.
Food is an ideal medium for the proliferation of infective agents. Unhygienic practices such as neglecting to wash one's hands when working with food, cross-contamination of foods in the same kitchen, inadequate cold-storage facilities, and repeated reheating of foods all contribute to microbiological growth.
In these cases, diarrhoea may have a positive effect in that it helps to rapidly expel dangerous microbes from the digestive tract.
- Viral infection is probably the most common cause of short-term diarrhoea. A virus damages the mucous membrane lining the intestine and disrupts fluid absorption. Rotavirus is often the cause of diarrhoea in children under two. Norwalk virus is more common in adults, and usually results from drinking contaminated water or food.
- Bacteria in contaminated food or water produce toxins that trigger intestinal cells to secrete salt and water, resulting in diarrhoea. Salmonella, Campylobacter, Listeria and Shigella are serious foodborne bacterial infections that require medical evaluation. Diarrhoea caused by E. coli most often occurs in visitors to developing countries where sanitation is poor. Cholera, which has acute diarrhoea as one of its symptoms, is contracted mainly by drinking contaminated water.
- Parasites such as amoeba and giardia can attack the intestine. Giardia may occur in wild animals and contaminated water. Giardiasis usually infects young children, often in day care, where it is transmitted by direct contact, or by adults changing different children’s nappies without hand washing. Giardiasis can last months without treatment and spreads rapidly. Testing all contacts is important, as some people spread the infection without having diarrhoea themselves.
- HIV-positive individuals are also at risk of other opportunistic infections that can cause diarrhoea, e.g. cryptosporidium and isospora belli.
Non-infectious diarrhoea
• Food: Certain foods may cause diarrhoea in some people, for example large amounts of alcohol, caffeine, artificial sweetener, or fatty or spicy foods.
Many people are intolerant of the milk sugar lactose, due to lactase deficiency. Lactase is an enzyme that breaks down lactose to glucose, which is readily absorbed by the intestinal tract. Even small amounts of dairy products can cause diarrhoea in individuals with lactase deficiency.
• Medications: Diarrhoea can develop up to a month after taking antibiotics. Antibiotics change the gut microflora and can predispose to infection with a bacteria called Clostridium difficile, resulting in diarrhoea that can range in severity from a mild illness to life-threatening disease.
Many people become dependent on chemical laxatives such as milk of magnesia, magnesium sulphate (Epsom salts), cascara and phenolphthalein. Magnesium can be inadvertently ingested in certain over-the-counter products. Sorbitol, an artificial sweetener used in some products such as jams, is also a laxative.
If diarrhoea occurs after taking a new medicine, contact your doctor.
• Diseases: Chronic diarrhoea can be caused by intestinal disorders such as inflammatory bowel disease (including ulcerative colitis and Crohn's disease), chronic pancreatitis, coeliac disease, colon cancers and tumours of the small intestine. Microscopic colitis is an unusual condition which causes diarrhoea in elderly people. These are serious diseases requiring medical attention.
Irritable bowel syndrome (IBS) is a very common cause of diarrhoea and occurs when the intestine does not contract smoothly and rhythmically. The contractions can be too strong, causing diarrhoea, or too weak, causing constipation. There may be alternating constipation and diarrhoea. IBS is associated with abdominal pain and bloating. Emotional stress may aggravate these symptoms.
Diabetes mellitus, kidney disease and a history of intussusceptions (where one portion of the bowel “telescopes” into the next) can also cause chronic diarrhoea.
